1. Field of the Invention
The present invention relates to an electromagnetic coupling apparatus for intermittently transmitting a rotational torque by utilizing an electromagnetic force, and more particularly to, for example, an electromagnetic coupling apparatus provided with a first rotary member for forming a magnetic circuit, a magnetically exciting coil provided rotatably relatively inside of the first rotary member, a yoke provided rotatably relatively to the first rotary member for constituting a part of the magnetic circuit of the first rotary member, and a second rotary member provided to face the first rotary member in an axial direction and having a movable member and provided to be movable in the axial direction for constituting a part of the magnetic circuit.
2. Description of the Related Art
A conventional electromagnetic coupling apparatus will now be described.
In a paper feed mechanism for a copying machine, a facsimile or the like, a paper feed roller is rotated from a predetermined rotational position by a predetermined angle, for example, one turn to feed a piece of recording paper into an interior of the apparatus. The electromagnetic coupling apparatus for performing engagement operation and interruption operation of a clutch is applied in accordance with a control of electric supply to electromagnets as a drive apparatus of a paper feed roller shaft in the paper feed mechanism.
FIG. 6 is a fragmentary side elevational view showing one example of such an electromagnetic coupling apparatus.
In FIG. 6, reference numeral 1 denotes the first rotary member. This rotary member is in the form of a ring for forming the magnetic circuit having a U-shape in cross section and is composed of a cup-shaped rotor 3 and a first shaft 2 made of oil impregnated sintered alloy into which a suitable amount of oil is impregnated.
Reference numeral 4 designates the magnetically exciting coil. This magnetically exciting coil 4 is an annular coil that is disposed inside of the first rotary member 1, i.e., between the first shaft 2 and the rotor 3 to be movable relative to the first rotary member 1 and wound around a bobbin 12 that is a winding frame.
A yoke 5 is disposed on the opening end side of the first rotary member 1, i.e., on the open side of the gap between the first shaft 2 and the rotor 3 to form a part of the magnetic circuit, mounted to be slidable, i.e., movable in the axial direction and rotatable relative to the first shaft 2 and made of oil impregnated sintered alloy into which a suitable mount of oil is impregnated.
A second rotary member 6 is disposed to face the first rotary member 1 in the axial direction, fixed to a gear portion 7 through a leaf spring 8 to form a part of the magnetic circuit and composed of a movable member 9 that is movable in the axial direction.
A second shaft 10 is made of oil impregnated sintered alloy into which a suitable amount of oil is impregnated, clamps the rotor 3 in cooperation with the first shaft 2. The first shaft 2 and the second shaft 10 are formed into one piece by press-fitting or by invasion of a projection (not shown).
A rotation preventing projection 5a that forms a rotation preventing means relative to the first rotary member 1 is provided at a part of the yoke 5 and is connected to or engaged with an outside stationary portion (not shown) so that the yoke 5 and the magnetically exciting coil 4 are prevented from rotating together with the first shaft 2.
Also, the movable member 9 is positioned to have a gap G between the movable member 9 and the side surface of the rotor 3 in the case where one end of the gear portion 7 is brought into contact with a side surface of the rotor 3.
A plurality of windows (not shown) are formed in the side wall portion that serves as a frictional surface with the rotor 3 to increase the magnetic resistance to decrease a part passing through the side wall portion from an inner diameter side to an outer diameter side of the rotor 3 and to increase a part passing through the movable member 9 out of the magnetic flux "PHgr" to be described later.
Also, the above-described first shaft 2, second shaft 10 and yoke 5 are formed of the oil impregnated sintered alloy into which the oil is impregnated in order to form the magnetic circuit and the rotor 3 and the movable member 9 are made of magnetic material, for example, iron plates.
The operation of this electromagnetic coupling apparatus will now be described.
When the rotational torque of the drive shaft (not shown) is transmitted to the second rotary member 6 through the gear portion 7, the second rotary member 6 inclusive of the movable member 9 is rotated around the second shaft 10.
Subsequently, when the current is caused to flow through the magnetically exciting coil 4 as the magnetically exciting means to magnetically excite the coil, the magnetic flux "PHgr" passing through the first shaft 2, the side wall portion of the rotor 3, the movable member 9, the cylindrical portion of the rotor 3 and the yoke 5 is generated to form the magnetic circuit.
The movable member 9 is attracted to the side wall portion of the rotor 3 against the spring force of the leaf spring 8 by the thus generated magnetic force. The rotational torque is transmitted between side surfaces of the movable member 9 and the side wall portion of the rotor 3 by the force that is determined by the attractive force and the frictional coefficient between the movable member 9 and the rotor 3.
Accordingly, the rotational torque given to the second rotary member 6 is transmitted to the first shaft 2 through the leaf spring 8, the movable member 9 and the rotor 3 so that the load shaft of the load device (not shown) engaged with the first shaft 2 is drivingly rotated.
On the other hand, when the electric supply to the magnetically exciting coil 4 is interrupted, the electromagnetic force is eliminated and the movable member 9 is separated away from the rotor 3 by the restoration force of the leaf spring 8. As a result, the rotational torque of the second rotary member 6 is not transmitted to the first shaft 2 and is not transmitted to the load shaft (not shown). Thereafter, the load device (not shown) is naturally stopped by, for example, a mechanical frictional force or the like.
As described above, in the conventional electromagnetic coupling apparatus, the first shaft 2 and the yoke 5 are made of oil impregnated sintered alloy into which the suitable amount of oil is impregnated. For this reason, there is a limit to durability (anti-sliding property). There is a problem that a disadvantage of sticking or the like is generated due to the degradation of the oil or the shortage of the oil, resulting in locking or that the inertia rotation of the load is remarkable, or that the amount of wear of the sliding portions is increased.
Also, the yoke 5 made of the oil impregnated sintered alloy tends to be magnetically balanced with rotor 3 to be attracted toward the rotor 3 and to be subjected to a thrust load. The magnetic exciting coil 4 is pushed toward the side wall portion of the rotor 3 so that the bobbin 12 that is the winding frame of the magnetically exciting coil 4 is frictionally moved on and along the side wall portion of the rotor 3 to increase the frictional wear amount of the end face of the bobbin 12. Furthermore, there is a problem that a stick slip is generated between the side surfaces of the bobbin 12 and the rotor 3 by the frictional wear powder so that the bobbin is resonant and generates abnormal noise.
Also, when the yoke 5 tilts when the yoke S is attracted toward the rotor 3, the sliding portion thereof with the first shaft 2 is abnormally worn.
Also, since the first shaft 2, the second shaft 10 and the yoke 5 are made of oil impregnated sintered material, these components are porous. Due to the existence of these pores, the density is lowered and the magnetic resistance is increased. As a result, it is difficult to obtain the static frictional torque. In particular, since it is necessary to impregnate the yoke 5 with a suitable amount of oil in order to maintain the oil content, it is impossible to increase the density.
Also, in order to improve the sliding property, it is necessary to add copper (Cu). However, for this reason, it is impossible to improve the magnetic characteristics and it is difficult to increase the torque.
In addition, since it is difficult to increase the static frictional torque, it is necessary to reduce the clearance of the adjacent components to decrease the magnetic resistance. For this reason, there is a problem that the magnetic shielding property is further degraded. If the magnetic shielding property becomes worse, the paper is fed too much, which leads to the paper jam.
Also, if the projection portion is provided outside of the first rotary member 1 as the rotation preventing means for the yoke 5 to the first rotary member 1, the length thereof is elongated because the rotary member is made of sintered alloy.
Also, in case of oil impregnated sintered material, its manufacture process is complicated and costly.
With respect to the yoke 5, Japanese Examined Patent Publication No. Sho 52-26294 and Japanese Examined Patent Publication No. Sho 57-23815 disclose a yoke (iron core) that is not made of oil impregnated sintered material but formed of laminated thin plates in the circumferential direction.
However, in these cases, since after the respective thin plates are aligned uniformly, the resin is caused to flow in between the thin plates, there is a serious problem that the magnetic characteristics become worse.
If, in order to improve the magnetic characteristics, the resin containing the magnetic powder is used, there is a problem that the manufacture cost is considerably increased.
In order to overcome the above noted various problems, an object of the present invention is to provide an electromagnetic coupling apparatus that is superior in durability with a high performance.
According to a first aspect of the present invention, there is provided an electromagnetic coupling apparatus comprising: a first rotary member constituting a magnetic circuit; a magnetically exciding coil provided to be relatively rotatable inside of the first rotary member; a yoke provided to be rotatable relative to the first rotary member for constituting a part of the magnetic circuit of the first rotary member; and a second rotary member provided to face the first rotary member in the axial direction and having a movable member provided to be movable in the axial direction for constituting a part of the magnetic circuit, wherein the yoke is formed by laminating thin plates in the axial direction.
According to a second aspect of the present invention, there is provided an electromagnetic coupling apparatus comprising: a first annular rotary member constituting a magnetic circuit having a U-shape in cross section; a magnetically exciding annular coil provided to be relatively rotatable inside of the first rotary member; an annular yoke disposed on an opening end side of the first rotary member, provided to be rotatable relative to the first rotary member for constituting a part of the magnetic circuit of the first rotary member; and a second rotary member provided to face the first rotary member in the axial direction and having a movable member provided to be movable in the axial direction for constituting a part of the magnetic circuit, wherein the yoke is formed by laminating annular thin plates in the axial direction.
According to a third aspect of the present invention, in the electromagnetic coupling apparatus according to the first or the second aspect of the present invention, a resin bush is provided between the yoke and the first rotary member.
According to a fourth aspect of the present invention, in the electromagnetic coupling apparatus according to the third aspect of the present invention, the resin bush and a winding frame of the magnetically exciting coil are formed integrally with each other.
According to a fifth aspect of the present invention, in the electromagnetic coupling apparatus according to the third or the fourth aspect of the present invention, the resin bush is fixed to the yoke.
According to a sixth aspect of the present invention, in the electromagnetic coupling apparatus according to the fifth aspect of the present invention, an engagement convex portion is provided on an outer diameter side of the resin bush and an engagement concave portion engaged with the engagement convex portion is provided on an inner diameter side of the yoke.
According to a seventh aspect of the present invention, in the electromagnetic coupling apparatus according to the sixth aspect of the present invention, the engagement convex portion is a rib formed on the outer diameter side of the resin bush and the engagement concave portion is a cutaway engaged with the rib of the resin bush and provided on the inner diameter side of the yoke.
According to an eighth aspect of the present invention, in the electromagnetic coupling apparatus according to the seventh aspect of the present invention, the rib of the resin bush is thermally deformed at the cutaway portion of the yoke opposite the magnetically exciting coil to fix the yoke and the resin bush together, and the yoke and the magnetically exciting winding frame are formed integrally with each other through the resin bush.
According to a ninth aspect of the present invention, in the electromagnetic coupling apparatus according to the second aspect of the present invention, a diameter of the outer diameter portion that does not face the outer circumferential portion of the first rotary member is smaller than a diameter of the outer diameter portion of the yoke that faces outer circumferential portion of the first rotary member.
According to a tenth aspect of the present invention in the electromagnetic coupling apparatus according to the second aspect of the present invention, a part of the outermost thin plate of the yoke opposite the magnetically exciting coil is caused to extend radially outwardly to serve as a rotation preventing member for the first rotary member.
According to an eleventh aspect of the present invention, in the electromagnetic coupling apparatus according to the first or the second aspect of the present invention, corrugations of adjacent thin plates where the corrugations are provided and engaged with each other.
According to a twelfth aspect of the present invention, in the electromagnetic coupling apparatus according to the first or the second aspect of the present invention, a surface process for enhancing anti-wear proof and sliding property is applied to a sliding portion of the yoke.
According to a thirteenth aspect of the present invention, in the electromagnetic coupling apparatus according to the first or the second aspect of the present invention, holes of a predetermined form and arrangement are provided in each thin plate, and the form and the arrangement of the holes are of at least two patterns.
According to a fourteenth aspect of the present invention, in the electromagnetic coupling apparatus according to the first or the second aspect of the present invention, the thin plate to be laminated to the portion that does not face the outer circumferential portion of the first rotary member having a U-shape in cross section is made of non-magnetic material.
According to a fifteenth aspect of the present invention, in the electromagnetic coupling apparatus according to the tenth aspect of the present invention, the rotational preventing member for the first rotary member is formed by bending the thin plate toward the outside of the first rotary member having a U-shape in cross section.
According to a sixteenth aspect of the present invention, in the electromagnetic coupling apparatus according to the first or the second aspect of the present invention, a cutaway is formed in the inner circumferential side of the yoke and lubricant is filled in the cutaway.